Awareness of the potential of protozoan pathogens to cause disease in humans has led an increasing number of US health authorities to introduce surveillance programs for these organisms. While comprehensive surveillance mechanisms for infectious diseases are generally considered desirable, the introduction of new programs can be associated with some pitfalls. These include an apparent upsurge in the number of cases due to increased reporting levels (pseudo-outbreaks), and a higher rate of false positive reports of infection (pseudo-infections).
The Centers for Disease Control and Prevention in the US recently reported the outcome of investigations into two "outbreaks" of gastroenteritis attributed to protozoan pathogens (1).
The first outbreak occurred in a children's shelter in Florida in mid 1995, a few weeks after all state laboratories introduced routine staining for Cyclospora cayetanensis during parasitological testing of stool specimens. A total of 81 people were tested for protozoan pathogens after the initial diagnosis of Giardia cysts in the stools of a young child with gastroenteritis.
The testing laboratory reported 6 of 25 (24%) children were positive for Giardia, however Cyclospora oocysts were found in the stool specimens from 16/25 children (64%), 31/36 staff (86%), and 9/20 volunteer workers (45%). As a result of these findings, all of the children were treated with antibiotics and the shelter was temporarily closed to new residents.
Investigation by the Federal Health Department showed that the reporting of gastroenteritis symptoms was not significantly different between people with negative stool tests and people with positive tests. There was no association of positive tests or symptoms with presumed infection risks such as eating or drinking at the shelter, or taking part in field trips. There was no evidence of a general community outbreak in the area with only 2 specimens positive for Cyclospora out of 357 stool specimens tested at the local hospital over this period.
Confirmatory laboratory testing of 23 stool samples (17 positive and 6 negative according to the initial testing laboratory) was sought from laboratories at CDC and the University of Arizona. None of the specimens were confirmed as positive by the reference laboratories.
Stored slides from 130 other people diagnosed as having Cyclospora infection by the testing laboratory during 1995 were also examined by CDC - only 38 were confirmed as positive. The high rate of false positive diagnoses by the state branch laboratory was attributed to the presence of pollen grains and other artifacts which were mistakenly identified as oocysts by inexperienced and inadequately trained technicians.
The second outbreak took place in New York City, also in 1995. A commercial laboratory reported 281 positive tests for Cryptosporidium oocysts in stool samples over a 6 month period, compared to only 4 positives in the previous 15 months. The follow up of these cases by the NYC Department of Health surveillance system showed them to have different demographic characteristics from the majority of Cryptosporidium cases in the city. The majority of Cryptosporidium cases in New York occur in men and in the young adult age group, however the cases reported by this laboratory were mainly female and included a higher proportion of people over 60 years.
The commercial laboratory was asked to take part in a prospective validation study where stool specimens were split and a portion sent to one of two state laboratories for confirmatory testing. The results showed a high rate of false positive diagnoses by the commercial lab, with only 1 of 84 split specimens reported positive by the state laboratories compared to 57 of 84 by the commercial laboratory. The massive increase in false positive tests by the commercial laboratory was attributed to a change in testing method from acid-fast staining to an enzyme-linked immunosorbent assay.
These pseudo-outbreaks illustrate the problems associated with changes in surveillance programs and testing methods. The successful introduction of these new methods also requires adequate training of personnel and a system for validation of laboratory results by experienced reference laboratories. If such mechanisms are not in place, it is likely that substantial resources will be wasted investigating pseudo-outbreaks and pseudo-infections. In addition, the patients involved in such episodes may be subject to unnecessary medical treatment, leading to a loss of confidence in the public health system by both the public and health professionals.
1 Outbreaks of Pseudo-Infection with Cyclospora and Cryptosporidium - Florida and New York City, 1995. Morbidity and Mortality Weekly Report (1997) 46 (16) 354-358.
The March issue of the Journal of the American Water Works Association featured two articles presenting somewhat divergent views on New York City's water supply. The first article (1) was written by several members of an expert panel appointed by the US EPA in 1992 to evaluate whether the city could meet the requirements of the Surface Water Treatment Rule to avoid filtration of its water supply.
The panel spent several months reviewing the characteristics and management of the water supply system, before delivering a final report in March 1993 unanimously recommending against avoidance of filtration. The findings of the report were supported by four EPA scientific staff who had acted as a peer reviewers during the work of the panel.
However, despite the conclusions in the report the EPA granted New York City permission to avoid filtration until December 1993 and subsequently extended this date until 1996, 1999 and most recently until 2002. The reasons advanced by the panel for recommending filtration were as follows:
The second article was written by several city officials from the Department of Environmental Protection and other water supply agencies in New York (2). It briefly describes the historical development of the three reservoir systems that serve New York City and the characteristics of the watersheds, reservoirs, lakes and rivers that comprise them. The Croton system is the oldest and presently supplies about 10% of the city's water needs, the Catskill system supplies 40% and the Delaware system the remaining 50%.
The measures being implemented by the city under the series of agreements with the EPA relating to avoidance of filtration for the Catskill and Delaware systems are then discussed:
While the EPA and New York City have reached an amicable agreement over the avoidance of filtration for the Catskill and Delaware systems, legal action is pending over the Croton reservoir system. The Croton watershed is more heavily developed than the Catskill and Delaware systems, and in summer the reservoir is often bypassed because of high bacterial levels in the water.
The city entered into an agreement with the EPA in 1992, undertaking to filter the Croton water supply and fixing 1997 as the start date for construction. However lack of action on the issue led to the EPA commencing court action in April this year to force the city to honour its commitment to filtration.
According to an article in The New York Times on 12th May, New York mayor Rudolph Giuliani is arguing that watershed protection measures now being implemented are sufficient to improve water quality. Sceptics have pointed out that there is strong local opposition to the proposed site of the filtration plant - a reservoir park in the Bronx district, and suggested that the pending mayoral election campaign may explain the city's delaying tactics.
1 New York City: To filter or not to filter? Okun DA, Craun GF, Edzwald JK, Gilbert JB and Rose JB (1997). J AWWA 89 (3) p62-74.
2 Watershed protection for New York City's supply. Ashendorff A, Principe MA, Seeley A, LaDuca J, Beckhardt L, Faber W Jr and Mantus J (1997) J AWWA 89 (3) p75-88.
INTERNATIONAL SYMPOSIUM ON WATERBORNE CRYPTOSPORIDIUM
2-5 March 1997, Newport Beach, California.
This symposium was attended by Peter Scott and Shane Haydon of
Melbourne Water, who have provided this overview of the main topics.
The symposium ran five major sessions: Detection, Occurrence,
Communication, Treatment, and Risk & Epidemiology over a three
day period. The major points made at the symposium were:
Detection
Accurate measurement of Cryptosporidium is still extremely difficult and is likely to continue this way for the foreseeable future. New methods are under development but are several years away from becoming standard techniques.
Several researchers have cautioned water utilities about putting too much faith in low levels of detection.
At present there appears to be no suitable surrogate for Cryptosporidium.
PCR analysis for Cryptosporidium is sensitive down to 10 oocysts but does not indicate viability.
Routine monthly monitoring will give a reasonable indication of median levels of Cryptosporidium but will give a poor indication of rare or extreme events which could be the cause of a Cryptosporidium-induced gastrointestinal disease outbreak.
Monthly sampling usually misses spikes of Cryptosporidium and Giardia, therefore not truly representative of peaks - highly skewed data, peaks may be up to 10 times averages. Monthly data is a good indicator of median but poor indicator of 90th percentile.
Implementation of the US EPA Information Collection Rule (ICR) from July 1997 to December 1998, will cost about $100 (US) Million. However there is much doubt as to the value of the data that will be collected.
Occurrence
Livestock, particularly the young, appear to be major reservoirs of the disease (ie supports closed catchment arguments).
1 gram of manure from a young calf can give 10 to 30 million oocysts (which is more than estimated daily output of older cattle). Therefore this points towards calving management options having a high impact on catchment contamination.
Birds etc can be "mechanical" vectors of Cryptosporidium parvum, ie: Cryptosporidium parvum cannot grow in these hosts but they can carry the cysts. If birds ingest oocysts while scavenging for food, the oocysts can remain viable and be excreted at a new site. Seagulls may be involved in mechanical transfer of Cryptosporidium parvum, and may be a significant source of reservoir contamination eg: 100,000 to 200,000 seagulls have been recorded on a London reservoir.
Oysters and other shellfish are also potential vectors, they filter up to 10 litres of water /hr, remove Cryptosporidium oocysts and Giardia from water, so may also serve as a mechanical vector. These observations on birds and shellfish come from laboratory experiments - neither birds or oysters have had Cryptosporidium parvum detected from natural infection.
A survey of 55 reservoirs >100 acres in area showed that 36% did not allow any recreation and 24% allowed no body contact in the water. Relative difference between reservoirs with no body contact and those with no recreation is an order of magnitude in terms of Cryptosporidium levels in the water.
Communication
Public confidence in potable water supplies is falling due to
Cryptosporidium outbreaks.
Cryptosporidium is the issue for the water industry in Northern America, at present, much bigger than in Australia.
The American Water Works Association Research Foundation (AWWARF) has put in place a 5 year US $19 million research program which comprises 67 projects on Cryptosporidium. A total of 9 projects (US$ 1.15 million) have been approved for 1997. Cryptosporidium is the number one research priority for AWWARF at present.
Treatment
Chlorine will give a kill at 4 mg/l and 120 minutes contact time
Advanced and pulsed UV shows some promise, with at least 2 log inactivation being achieved. Based on animal infectivity studies this could go to 4 log inactivation.
Ozone is being considered by many US authorities for Cryptosporidium inactivation.
Risk and Epidemiology
Cryptosporidium outbreaks have occurred in UK, USA, Canada
and Japan.
A level of 1: 10,000 for acceptable risk (ie 1 person in 10,000 per year) of developing cryptosporidiosis is still being generally used although some now consider it to be too stringent.
There is generally a low level of reporting for immuno-competent people where cryptosporidiosis is not life threatening, however in the immuno-compromised population the level of reporting is very high (0.07% vs 69% in one study undertaken by Columbia University on New York) due to the high likelihood that infection may be severe and possibly life threatening.
AIDS/ HIV+ patients are not good indicators of baseline infection in the community as their physicians are more aware of Cryptosporidium and will seek more diagnostic tests than other doctors.
The predicted annual risk of catching Cryptosporidium is 0.1 to 1 % for non-AIDS patients and 0.2 to 2% for AIDS patients assuming oocysts in the range 0.001 to 0.01 /litre. These predicted rates are 100 to 1000 times the reported rate of cases due to the low proportion of people who consult a doctor over Cryptosporidium.
Approx 0.07% of non-AIDS Cryptosporidium infections will be reported compared to 69% of AIDS patients. Real case reporting is in the range of 10 to 100 cases per 100,000/yr.
Further volunteer feeding studies have been done by the Dupont group in Texas. In the first study 29 healthy adults without detectable antibodies to Cryptosporidium parvum were challenged with 30-1,000,000 oocysts, and 18 (62%) became infected (oocysts detected in faeces), although only 7 had diarrhoea and 4 had other enteric symptoms (two publications arising from this study were summarised in Health Stream Issue 2 June 1996).
The development of antibodies by the exposed volunteers did not correlate with symptoms or oocyst shedding, with 73% developing IgM, 45% developing IgA and 21% developing IgG. From this study it was estimated that the ID50 (dose resulting in 50% of people becoming infected) was 130 oocysts, and the ID10 was 30 oocysts. Development of symptoms was independent of dose rate.
One year after the first exposure, 19 of these volunteers were challenged with 500 oocysts from the same Cryptosporidium parvum isolate. By this time only 1 of the 19 still had detectable antibodies to Cryptosporidium. On the second exposure 7/19 developed diarrhoea but only 3 shed oocysts.
More experiments have been carried out with volunteers who were already antibody positive - the results of these studies indicate that the ID50 is of the order of 5000 to 8200 oocysts, or about 37 fold higher than for antibody negative volunteers. Therefore it appears that the presence of circulating antibodies indicates resistance to infection with low numbers of oocysts.
Volunteer studies are continuing with different isolates of C. parvum, to assess the degree of variability in pathogenesis in humans.
ASID CONFERENCE
The Annual Scientific Meeting of the Australasian Society for
Infectious Diseases was held in Queenstown, New Zealand in March.
Dr Margaret Hellard of DEPM presented a poster at the conference,
and the abstract is reproduced here by permission of ASID.
Gastroenteritis in Australia: who, what, where, and how much?
Hellard ME, Veitch MKG and Fairley CK.
Introduction: Limited data are available on the impact
of endemic gastroenteritis on the health of Australians, its socioeconomic
impact, and the relative contributions of various organisms to
endemic disease. We aimed to use available data to estimate the
burden of gastroenteritis in Australia, and identify the key related
public health issues.
Methods: We used local data (Australian Sentinel General Practice Scheme, 1989-90 National Health Survey), and published surveys from Australia and overseas, to estimate the crude incidence of gastroenteritis in Australia. Four private pathology services based in Melbourne also provided data on the yield of faecal testing over a one month period in 1996.
Results: We estimated that between 4.6 and 12.8 million cases of gastroenteritis occur each year in Australia. Approximately half the episodes of illness resulted in a day or more absent from work or school. A survey of four private laboratories in Melbourne over a period of one month indicated the pathogens most commonly identified by the laboratories were Campylobacter (3 to 8% of samples), Salmonella (1 to 5%), Giardia (2 to 4%), and Cryptosporidium (1 to 2%).
Conclusion: Endemic gastroenteritis causes vastly more disease than do documented outbreaks. Indicators of the morbidity, mortality, and socioeconomic impact of gastroenteritis should be sought, along with investigations to identify sources and routes of transmission for potentially preventable infections.
For further details on the data presented in the above abstract, refer to the editorial "Gastroenteritis in Australia: who, what, where, and how much?" by ME Hellard and CK Fairley in the Australian and New Zealand Journal of Medicine 27 (1997) p147-149.
Relative Risk and Odds Ratios - tools to measure the association between an exposure (a potential risk factor) and a disease.
The aim of many epidemiological studies is to find out if there is an association between an exposure and a disease and to estimate the strength of this association.
For example:
Relative Risks and Odds Ratios are two important ways of expressing the strength of association between an exposure and a disease.
Relative Risk is used in intervention studies and in cohort studies. For a description of these type of studies refer to Health Stream Issue 1 April 1996 and Issue 2 June 1996.
Odds Ratio is used in case control studies or cross-sectional studies (refer Health Stream Issue 3 Sept 1996). Theoretically one could use an odds ratio measurement in an interventional or a cohort study but in practise this is not often done.
Relative risk:
A relative risk is simply a relative incidence. It is the incidence or number of new cases of a disease (per 1,000 individuals) in a group of individuals exposed to a factor, compared to the incidence, or number of new cases of a disease in a group of individuals not exposed to the factor.
If the relative risk is two, it means that the disease occurs twice as commonly in those exposed to the factor than it does in those not exposed to the factor.
For example:
If we define incidence in the exposed (IE) and the incidence in the unexposed (IO) then the Relative Risk (RR) is
RR = IE/IO
For example:
If the incidence (or risk) of developing lung cancer if you smoke (IE) is ten times greater than the incidence (or risk) of developing lung cancer if you don't smoke (IO) the relative risk (RR) is 10.
Odds Ratio:
An Odds Ratio is used in case control studies because it is not possible to calculate the incidence of disease. This is because to calculate the incidence of disease, the number in the population from which the cases developed must be known but in case control studies the total population is not know.
The term Odds Ratio is used to overcome this problem and provide a measure of the strength of the association between a risk factor and a disease. The Odds Ratio is the odds (or chance) of exposure among the cases (ie those with the disease) compared to the odds (or chance) of exposure among the controls (ie those who do not have the disease).
OR = Odds of Exposure in Cases
Odds of Exposure in Controls
This is not the same as a relative risk, which can be interpreted as meaning that one is so many times more likely to develop a disease if you are exposed compared to if you are not exposed. In most cases however the Odds Ratio is essentially equivalent to a Relative Risk if the disease is rare. When a disease is not rare however, the Odds Ratio will over estimate the Relative Risk.
Because lung cancer is rare, it is true to say that if a case control study found that the Odds of smoking (Ratio) was 10 times greater for cases compared to controls, then it is true to say that the smokers are 10 times more likely to develop lung cancer than non smokers. This is not however true for a common disease.
Lets consider the example of gastroenteritis which is common. In this example we will define a case as someone who has had gastroenteritis in the last year, and a control as someone who has not. We find in the study that the Odds of having a child at creche is 3 times higher if you are a case than a control. The Relative Risk using similar numbers however would be 1.7, implying that individuals with a child in creche are only 1.7 times more likely to get gastroenteritis than those without.
Association versus causation
It is important to understand that both Odds Ratio and Relative Risk measure the strength of association between an exposure and a disease. They do NOT imply that the disease is CAUSED by the exposure. In some instances a causal link will exist, and in others it will not. This problem is relevant to the association between chlorinated drinking water and bladder cancer found in some studies.
In the next issue of Health Stream we will deal with the inference of causation.
Australians on WHO Cyanobacteria Taskforce
Two Australian scientists are members of the World Health Organisation
Taskforce on Cyanotoxins, which is working to develop guidelines
for cyanobacterial toxins in drinking water. Professor Ian Falconer
of the University of Adelaide, and Dr Jim Fitzgerald of the South
Australian Environmental Health Department recently visited Germany
to confer with other international experts on the taskforce.
Professor Falconer leads the CRCWQT project on Cyanobacterial Tumour Promotion, and has just completed a 5 year term as Deputy Vice Chancellor at the University of Adelaide. The German meeting also included experts from the US, UK, and Canada, and focussed on formulating an agreed approach to "Tolerable Daily Intakes" and water guideline values for cyanobacterial toxins.
London Cryptosporidium outbreak ends
The Cryptosporidium outbreak near London officially ended
on 19th March following the lifting of the boil water advisory
to consumers. More than 300,000 households were affected by the
notice which was in force for 16 days. The Three Valleys water
company will pay £10 to each affected household as a goodwill
gesture for the inconvenience experienced during this period.
The source of the Cryptosporidium contamination was traced to a deep bore hole which had been contaminated by animal waste. Nearly 300 cases of cryptosporidiosis were confirmed by laboratory tests, and many other people may have been affected without seeking medical attention.
The Three Valleys water company is expected to face prosecution by the Drinking Water Inspectorate, and legal action from people seeking compensation for their illness.
Jet sewage hazards
A paper presented at the recent General Meeting of the American
Society for Microbiology in Florida, warned of the risks of sewage
waste from jet aircraft spreading infectious diseases around the
world. Dr Mark Sobsey summarised the findings of an investigation
into the survival of enteric viruses in 40 sewage samples discharged
from planes landing at 2 major US airports.
The study was funded by the World Health Organisation and the Centers for Disease Control, as part of a program to determine whether live polio viruses could spread from country to country in this way. The findings were featured in the 17 May edition of the New Scientist under the headline "Jetsetters send festering faeces round the world".
While no evidence of live polio virus was found in the tests, 19 of the 40 samples contained other human enteric viruses capable of infecting tissue cultures. The sewage samples had been treated with ammonium based disinfectants, but this had failed to inactivate the viruses. Dr Sobsey advocated the addition of glutaraldehyde to disinfection procedures to increase viral safety, and suggested that pathogenic bacteria and protozoa may also survive current disinfection procedures.
Safe to flush
Have you ever been worried about whether flushing your loo produces
dangerous aerosols of bacteria? Well, someone has been - researchers
from the University of Nevada have reported a series of experiments
aimed at measuring the potential of toilets to spread contaminated
aerosols when flushed. After spiking the toilet water with 106
bacteria per ml, air samples from seat height and breathing zone
level were taken at flushing and 15 minutes later. The researchers
concluded that modern residential and commercial toilets do not
produce significant aerosols, although they may intermittently
produce droplet splashes that contaminate bathroom surfaces.
EPA evaluates new water treatment technology.
It was reported in the May edition of Environmental Health thatthe US EPA has signed a 2 year agreement with a water treatment
company to evaluate a new water treatment method to inactivate
Cryptosporidium. The cooperative R&D agreement will
test a method that combines ultrasonic and electromagnetic fields
with UV irradiation. The technology has already been patented
by the company, and the testing program will evaluate the performance,
ease of use and costs of the system for conditions typical of
small community drinking water supplies.
Water firms accused of shock risk
British water companies moving to introduce water meters and "pay
by volume" charging structures have been accused of placing
families at risk of electrocution, according to the 16th May edition
of the Electronic Telegraph. Many older British homes are earthed
through the mains water pipe, and replacement of part of this
pipe with plastic during meter installation removes the earthing
capacity. Thames Water has responded to the criticism by supplying
electrical bonding strips to bridge the gap.
UK Farmers fight nitrate law
British farmers from Suffolk and Essex will go to the European
Court to challenge new laws governing "nitrate vulnerable
zones" in their districts. The zones are designed to limit
the levels of nitrates in drinking water, but farmers claim that
agricultural pollution has been unfairly singled out when sewage
and industrial effluent may be responsible for part of the problem.
The farmers claim that the value of farmland in the affected region had fallen by as much as £100 million as a result of the new regulations, and some may be forced out of business. The British High Court has granted leave for the case to be taken to the EU Court.
Holy Communion not a health risk
Speculation on the health hazards of sharing a communal cup of
wine during Holy Communion may be resolved by a recent study reported
at the 97th General Meeting of the American Society for Microbiology.
In a 10 week study of 681 people, no significant differences
in self reported health status were found between those who received
the sacrament, those who attended church without receiving communion,
and those who never attended church. Analysis of various risk
factors showed that living with a child under 12 increased the
risk of illness, while taking communion as frequently as every
day did not.
The Water Quality Study was described in our first issue in April 1996, under the name of The Water Filter Trial. The study will test whether point of use treatment of drinking water to remove microorganisms reduces the incidence of gastroenteritis in an area served by a disinfected but unfiltered water supply. A randomised controlled double blind study design is being used, with the 600 participating families being randomly assigned to receive either a real or a sham water "filter" (or more correctly a water treatment unit).
An adult member of each participating family will keep a Health Diary recording symptoms of gastroenteritis experienced by family members over a 15 month period. At the end of the study, the incidence of gastroenteritis in the two groups (real filter and sham filter) will be compared.
Much of 1996 was devoted to detailed planning of the study, and finalising the technical requirements for the water treatment units. The units were selected following a public tender process, with the contract for supply, installation, maintenance and removal of the units being won by an Australian company.
The water treatment units comprise a filter component with 1 micron absolute rated cartridge plus a UV treatment chamber. Sham water treatment units are identical in outward appearance to real units but are designed not to remove microorganisms.
The study is being jointly funded by the CRCWQT, WSAA, Melbourne Water, City West Water, South East Water, Yarra Valley Water and the Department of Human Services Victoria.
The recruitment phase of the study began in February 1997, with the commencement of an invitation mailout to residents in several suburbs in the southeast of Melbourne. Potential participants were also approached by means of pamphlets distributed through primary schools, kindergartens, preschools and creches, and Maternal and Child Health centres. The Study has been the subject of articles in the Sunday Herald Sun and several suburban newspapers.
Adult participants are requested to provide blood samples at
the beginning, middle and end of the study. These samples will
be tested for antibodies to potentially waterborne microorganisms.
Research Nurse Kimberley Gibson collects a blood sample from a
participant in the Water Quality Study.
Participants go through a 2 stage screening process before being enrolled by a Research Nurse who visits them in their home. Four Research Nurses are working on the project, and each will be responsible for maintaining contact with 150 families throughout the study. The first 50 families have had their water treatment units installed and are now taking part in a 6 week Pilot study. Meanwhile, recruitment of participating families continues at a steady pace and the main study will commence in September this year.
Recreational exposure to cyanobacteria
Research workers from the CRCWQT recently completed a epidemiological study of the health effects of recreational exposure to cyanobacteria. Dr Louis Pilotto and Prof Robert Douglas from the National Centre for Epidemiology and Population Health, and Mr Mike Burch from the Australian Water Quality Centre carried out the collaborative project in three states.
The study was designed to systematically collect data on the health status of people exposed to cyanobacteria in the course of common recreational activities such as swimming, wind surfing and water skiing. Our current knowledge of the effects of cyanobacterial exposure is largely based on anecdotal evidence, and no guidelines or regulatory standards have yet been developed. Thus water and health authorities are placed in a difficult situation with regard to restricting access to contaminated bodies of water.
The water and health authorities collaborating in the study included the South Australian Water Corporation, the South Australian Health Commission, the NSW Department of Health, the NSW Department of Land and Water Conservation, the NSW Environmental Protection Authority and the Victorian Department of Human Services.
The study involved 6 sites in three states, with 852 people taking part over 3 months. Participants were questioned about recreational activities involving water contact and a variety of symptoms including respiratory, gastrointestinal, eye, ear and skin ailments. The results suggest that the likelihood of adverse symptoms increases with length of water contact, and effects may occur at less than 20,000 cyanobacterial cells per ml (the level currently used by some Australian authorities as a trigger for action to restrict public access).
The study will be published shortly in the Australian and New Zealand Journal of Public Health, and the results are being used by the World Health Organisation expert committee which is working to develop guidelines for recreational exposure to cyanobacteria.
Management Committee Meeting
Date and venue of the next meeting of the Management Committee of the CRCWQT - to be announced.
Board of Management
The next meeting of the Board of Management of the CRCWQT will take place on 8th September in Adelaide.
Contact Information
| Editor - Martha Sinclair | email martha.sinclair@med.monash.edu.au |
| Assistant Editor - Pam Lightbody | email pam.lightbody@med.monash.edu.au |
The printed version of Health Stream is available free of charge - to be added to our mailing list please contact Pam Lightbody (email above or fax + 61 3 9903 0576).